The study of dispersed metals has a long history because of their use as catalysts. It is well-known in the art that as the size of the metal particles decrease, the activity increases. Mainly papers concerning the ratio of hydrogen to palladium atoms and the heats of adsorption of hydrogen into palladium are referenced herein. The rate of organic chemical bond-forming and cracking reactions also vary with particle size, as is well-known in the art. However, that art does not concern the present application. Much of the art references hydrogen reactions, but for the purpose of the present application, hydrogen and deuterium are considered identical in chemical nature for the ratios of uptake with a metal catalyst. For example, others have shown that the uptake of hydrogen increases rapidly when the particle size of the dispersed palladium in an oxide matrix decreases to 1 nm or less. See, e.g., Shu-Chin Chou et al., “Isosteric Heat of Sorption of Dihydrogen on Alumina-supported Palladium,” J. Chem. Soc. Faraday Trans., 91, 949-951 (1995); Sheng-Yang Huang et al., “Chemical Activity of Palladium Clusters: Sorption of Hydrogen,” J. Phys. Chem. B, 110, 21783-21787 (2006), the entire contents of each are incorporated herein by reference. Although, they did not state the particle size specifically, data from Huang, et al., can be used to estimate the particle size and the approximate ratio of H:Pd as shown in Table 1. The heat of adsorption also increased with decreasing particle size. Others have studied a number of supports and preparation conditions and have also showed that the heat of adsorption and loading ratio increased with decreasing particle size. Pen Chou et al., “Calorimetric Heat of Adsorption Measurements on Palladium I. Influence of Crystallite Size and Support on Hydrogen Adsorption,” J. of Catalysis, 104, 1-16 (1987), the entire contents of which is incorporated herein by reference. The estimated particle size in Chou's work was greater than 1.6 nm. Aben showed that hydrogen absorption could be used to estimate particle size and that the H:Pd ratio also increased with decreasing particle size, reaching a maximum H:Pd ratio of 0.83 in his study using ion exchanged silica. P. C. Aben, “Palladium areas in supported catalysts: Determination of palladium surface areas in supported catalysts by means of hydrogen chemisorption,” Journal of Catalysis, 10 224-229 (1968), the entire contents of which are incorporated herein by reference. The smallest size that Aben measured was 2.5 nm. He also showed that high pretreatment temperatures increased particle growth, which would be detrimental to the present invention.
TABLE 1Estimated particle sizes and H/Pd ratios as calculated from Huang, et al.Note the sensitive dependence on the loading ratio with particle size.The more chemically accessible particles (>5 nm) show a loadingsimilar to bulk palladium of 0.6.Heat ofEstimatedHydrogenParticleAdsorptionRatio H:Pd @PreparationSize (nm)(kJ/mole)0.2 barPd Powder9940.551.86% Pd/SiO2 (IW)~4920.68  10% Pd/SiO2 (SG)1.11310.9  5% Pd/SiO2 (SG)11831.05
As the particle size must be small for high H:Pd ratios, one must disperse the particles on a support to keep them from sintering and growing too large. As noted by P. A. Sermon, even heating palladium black (a non-supported form of nano-sized palladium) to 98° C. would cause sintering of the particles. P. A. Sermon, “Characterization of palladium blacks: I. A novel hydrogen pretreatment and surface area determination of palladium,” J. of Catalysis, 24, 460-466 (1972), the entire contents of which are incorporated herein by reference.
Arata (Arata et al., Formation of Condensed Metallic Deuterium Lattice and Nuclear Fusion. Proc. Jpn. Acad., Ser. B, 78 (Ser. B): p. 57 (2002), the entire contents of which is incorporated herein by reference) has claimed excess heat when pressurizing a specially-prepared Pd—ZrO2 or Pd—Ni—ZrO2 matrix (Shin-ichi Yamaura et al., “Hydrogen absorption of nanoscale Pd particles embedded in ZrO2 matrix prepared from Zr—Pd amorphous alloys,” J. Mater. Res., 17, 1329-1334 (2002), the entire contents of which are incorporated herein by reference). His particles (ca. 5 nm) are on the size level of commercial catalysts. See Yoshinori Arachi et al., “Alternation of the Pd Lattice in Nano-Sized-Pd/ZrO2 Composite during Hydrogen Absorption,” X-ray Absorption Fine Structure—XAFS13, edited by B. Hedman and P. Pianetta, 2007 American Institute of Physics, pp. 740-742 (2007); Yoshinori et al., “Structural analysis of nano-sized-Pd/ZrO2 composite after H(D) absorption,” Solid State Ionics 177, 1861-1864 (2006), the entire contents of each are incorporated herein by reference. Furthermore, they sinter during use. Others have attempted to put palladium in zeolites and expose it to deuterium to generate excess enthalpy. See I. Parchamazad et al., “Investigations of Nanoparticle Palladium/Deuterium Systems in Zeolites,” Abstract for 14th International Conference on Condensed Matter Nuclear Science”, Hyatt Regency, Washington, D.C. Aug. 10-15, 2008, the entire contents of which are incorporated herein by reference. The incorporation of the palladium was through an organic palladium precursor and the support was calcined before use—removing the organics and likely growing the particles. Parchamazad et al. made no mention of the particle size, cycling, nor amount of excess enthalpy was made.